In conventional direct-start methods, a fuel quantity that may be required for combustion may be injected into the combustion chamber of a cylinder whose piston may be in a working position, the injection taking place when the internal combustion engine is at standstill. The air-fuel mixture contained in the combustion chamber may be ignited within approximately 100 ms. The ignition of this air-fuel mixture represents the beginning of the so-called start phase, this, start phase being completed when idling speed is attained. The combustion of the air-fuel mixture at the beginning of the start phase may need to release sufficient energy to generate a torque at the crankshaft and to set it in motion in such a manner that in an internal combustion engine having a plurality of cylinders, for example, a piston of another cylinder is brought into working position. The energy generated during the combustion of an air-fuel mixture, made up of the air mass enclosed in the cylinder and the fuel quantity injected into it, is a function of the composition of the air-fuel mixture. Therefore, the carburetion may be of great importance, especially in a direct-start method without electromotive starter.
A warm start is made even more difficult in that, due to the air losing density with rising temperature, the charge of the cylinder is lower, which results in a reduced combustion torque.